1. Field of the Invention
The present invention relates to the crankcase structure of an engine. In particular, the present invention relates to the crankcase structure of an engine provided with a balancer.
2. Description of Background Art
In the background art, some engines mounted in a vehicle such as a motorcycle are provided with a secondary balancer. The secondary balancer is provided with a balancer shaft parallel to the crankshaft and is configured so that secondary engine vibration is effectively reduced by rotating the secondary balancer by two times the number of revolutions of the crankshaft (see JP-A-2000-310286). A balancer according to the above background art is configured by one or two shafts, and the layout is determined in consideration of a relation between the balancer and each part of the engine.
In the above-mentioned engine, the balancer is arranged in the front of the crankcase. However, in the case of a motorcycle for example, an exhaust pipe connected to the cylinder head is arranged so that the exhaust pipe passes the front side and the downside of the crankcase. Accordingly, there are many limitations on the balancer layout. In addition, an oil cooler and an oil filter are often arranged in the front of the crankcase and these including the balancer are required to be properly laid out.